Page last updated at 14:13 GMT, Wednesday, 20 May 2009 15:13 UK

Measurement science's odd pursuits

By Jason Palmer
Science and technology reporter, BBC News

Model ventilation system (NPL)
Testing a ventilation system on a model House of Commons

Wednesday marks World Metrology Day, commemorating the 1875 treaty introducing the Metre Convention, which has led to the metric system of units.

Since 1902, the body responsible for defining and standardising units in the UK - and the source of the radio "pips" famous for ticking off time - is the National Physical Laboratory (NPL) in Teddington, Middlesex.

Martyn Sene, director of NPL's Quality of Life division, says World Metrology day is the chance to "talk to people for one day about the things we do for the other 364 days of the year".

As he told the BBC, apart from the research that they do, NPL is often asked to lend its expertise to some unusual measuring jobs.

Skies and colour map (NPL)

Just where in the world is the bluest sky? Expedia wanted to know for its "Blue Sky Explorer" project. They asked NPL to develop a blue sky standard and some cheap equipment to measure it. Their solution was to use cheap light-emitting diodes as the light standard, rather than the typical expensive noble gas lamps, and the belt-and-braces device was calibrated against an international "colourimetry" standard.

The result? Rio de Janeiro came out on top, followed by the Bay of Islands in New Zealand and Uluru in Australia. Unsurprisingly the UK did not figure in strongly in the top 10, but Castell Dinas Bran in Wales came in at number nine.

Concorde wheel (NPL)

How much - precisely - does a supersonic jet weigh? Before the Concorde could be certified to fly commercially, that number had to be pinned down. In 1979, NPL took on the challenge, fitting scales under each of the wheels of the Concorde's landing gear.

The result? A sprightly 78,700 kg - without fuel.

Rice cake crunchiness measuring apparatus (NPL)

If there's one measure of quality control in a biscuit, it's how it crunches. But how to quantify crunchiness? When Stable Microsystems approached NPL with a snack-based concern, they were already producing their "Acoustic Envelope Detector" to measure the sounds from crunching and snapping foods.

They wanted to expand their range of expertise by finding out if foods make sounds above 12.5 kiloHertz and into the ultrasonic, beyond human hearing. They employed NPL's anechoic chamber - where no sound can echo - and exceptionally sensitive microphones.

The result? Rice cakes and biscuits do have characteristic noises in the ultrasonic, so it may be that your dog knows if your biscuits are fresh.

Smart car filled with balls (NPL)

How spacious is a Smart car? Among the many properties NPL measured, the total internal volume was among the trickiest.

"We considered filling the car with tiny plastic particles or even water to ensure we reached into every nook and cranny," said Nick McCormick, the NPL scientist in charge of the project.

"But it quickly became clear that we didn't need to use such excessive or potentially destructive approaches."

The team instead filled the car with fist-sized plastic balls as a reasonable estimate of the volume. The answer? Should you need to transport quite a few, a Smart car will hold 3,441 of them.

Electron micrograph of black surface (NPL)

Just how black can black be? Commercial black paints are, to the eye, pretty black indeed. But for optical applications, the ability to restrict reflections - even that last few tenths of a percent, can make the difference in telescopes and high-end imaging equipment.

To make the blackest commercially available coating the world has seen, NPL scientists experimented with a number of nickel/phosphorus compounds, and then chemically "etched" it with nitric acid. That creates a knobbly surface that minimises the amount of light reflected.

The result? For light incident at an angle, the surface reflects 25 times less light than the blackest of commercial paints.

Cauliflower (SPL)

NPL is currently working on developing the science that will lead to an intelligent harvesting machine - a robot harvester that knows when vegetables are ripe for the picking.

Annual wastage of some crops can be up to 60%, with an average farm's loss coming in at around £100,000. NPL is currently working with agricultural companies to develop imaging techniques that will peer under the foliage of, for example, cauliflower - whose readiness is impossible to determine before tearing the layers of leaves off.

But the technique is still being developed, so the measurement standard for cauliflower is still, sadly, under wraps.

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